The role of the frontal ganglion in locust feeding and moulting related behaviours.

In the desert locust, Schistocerca gregaria, the frontal ganglion (FG) plays a key role in control of foregut movements, and constitutes a source of innervation to the foregut dilator muscles. In this work we studied the generation and characteristics of FG motor outputs in two distinct and fundamental behaviours: feeding and moulting. The FG motor pattern was found to be complex, and strongly dependent on the locust's physiological and behavioural state. Rhythmic activity of the foregut was dependent on the amount of food present in the crop; animals with food in their crop demonstrated higher FG burst frequency than those with empty crop. A very full gut inhibited the FG rhythm altogether. When no feeding-related foregut pattern was observed, the FG motor output was strongly correlated with the locust's ventilation pattern. This ventilation-related rhythm was dominant in pre-moulting locusts. During the moult, synchronization with the ventilation pattern can be transiently switched off, revealing the endogenous (feeding-related) FG pattern. This presumably happens during vigorous air swallowing, and could also be induced experimentally. Our findings suggest that the FG central pattern generator can be modulated to generate a variety of motor outputs under different physiological conditions and behavioural contexts.